Textile printing is a localized dyeing, with one or two colors, of textile materials, such as fabrics, knitwear or non-woven fabrics, which allows to make drawings, writings, artistic representations or suchlike.
Printed textile fibers can be, for example, cellulose, animal, artificial or synthetic fibers and corresponding mixes thereof.
The dyes used can be the synthetic or natural type.
The synthetic dyes used can be reactive, direct, vat, acids, metalized acids, basic, disperse, corrodable dyes or pigments.
Natural dyes can be vegetable, animal or mineral in origin.
Textile printing provides to apply a printing paste of dyes or pigments and possible chemical auxiliaries to the textile material.
The printing paste can contain, as well as the dyes, also thickeners, hygroscopic or hydrotropic substances, such as for example urea, reagents such as for example acids, alkalis, reducers, sequestrants and various possible auxiliaries.
The application of printing paste can be made using square frames or engraved hollow cylinders.
A textile printing of the digital type is also known, in which a colored ink is applied on the textile material previously impregnated with the printing paste.
Following the application of the printing paste, mixed with the dyes and the corresponding chemical auxiliaries, the fabric is dried in controlled conditions so as not to alter the products applied.
Subsequently, a vaporization step is carried out, generally continuously at a temperature of 100° C. with saturated steam, on the dry printed support, so as to stably attach the dyes to the fiber.
During vaporization, the dye spreads in the fiber and is attached there, with the aid of the corresponding chemical auxiliaries.
The dye spreads, in particular, either with the action of the percentage of condensed water on the fiber, combined with that of the ambient heat, or simply through the intervention of the heat if super-heated steam is used.
The reduced percentage of water that condenses on the fiber depends on the temperature of the material entering, on the type of fiber and the presence of hydrotropic substances such as urea.
Vaporization with super-heated steam at a temperature of 150° C.-200° C. is applied with the purpose of attaching the prints consisting of disperse dyes applied to synthetic fibers, artificial fibers and possibly cellulose fibers or for pigment printing.
The most widespread vaporization apparatuses, commonly called vaporizers, are the continuous type, where the textile material travels as a suspended band.
Some disadvantages of using current vaporizers working continuously at atmospheric pressure are: poor yield of the dyes, long times required for attaching the dyes, for example 10-15 minutes in the case of reactive dyes applied to cotton, high consumption of printing paste and chemical auxiliaries, high consumption of urea, which is a highly polluting agent, high consumption of water in the washing step after vaporization.
Other disadvantages of current vaporizers are: high consumption of steam, formation of drops with consequent smearing of the print, delicate and difficult management of the apparatus.
In order to increase the dye yield positively on all types of fibers, thanks to the greater quantity of water that condenses on the fibers and to the high temperature, vaporization can be carried out under high pressure conditions, for example, adjustable up to 5 atmospheres and with a maximum temperature of about 150° C.
In this respect, HP (or high pressure) vaporizers are known, or star vaporizers, which work discontinuously, and HP machines that work continuously.
One disadvantage of HP star vaporizers is that they have very low productivity.
In the case of continuous HP machines, the dye yield is excellent but there are problems regarding the leakage of steam from the mechanical seals mounted at entrance/exit of the machine, which is risky for the users: there are also problems regarding wear on the seals, corresponding safety problems, cost and complexity of the machine.
In continuous dyeing or bleaching techniques the pad steam method is known, where the dyes or bleaching products are applied on the textiles using a “foulard” type device; they are then attached to the fibers using vaporization performed at a temperature of 100° C.
The counter-indications of this technique are: poor dye yield, need to have big lengths, high consumption of chemical auxiliary agents, high consumption of steam and water as well as the cost of the plant.
Document GB 729 353 A describes a method for attaching dyes applied on the textile material by means of a foulard type device, where the fabric enters between a felt and a heated drum. The heat vaporizes the liquid carried by the fabric; between the felt that is impermeable to steam and the hot surface of the drum, an environment is created at a temperature of about 100° C. The counter-indications of this technique are: poor dye yield, impossibility of attaching disperse dyes to polyester and limited processing speed.
Document U.S. Pat. No. 4,057,864 describes a print transfer method of the wet type. In this case, the textile material, previously wet, enters together with the transfer paper between an impermeable felt and a heated drum. The steam vaporizes the liquid carried by the fabric, so as to guarantee transfer of the dye from the printed paper to the textile material with subsequent attachment thereof to the fibers. To guarantee a steam atmosphere of above 100° C., on the external part of the strip a series of squeezer rollers are installed, which can exert, in the various points of contact with the strip, a high adjustable pressure such as to generate, in said points of contact, a steam environment with a pressure above atmospheric pressure. The counter-indications of this technique are: reduced contact surface between squeezer rollers and strip under high pressure conditions, so that the working speed is limited.
Document U.S. Pat. No. 5,173,980 describes a continuous decatizing method for wool fabrics. In this document, a humidified fabric enters between an impermeable felt and a hot drum. To vaporize the liquid in the fabric at a high temperature, higher than atmospheric temperature, a high longitudinal tension is applied to the impermeable strip. The counter-indications of this technique are: the non-uniform pressure of the strip against the textile material, which is considerably higher in the side opposite the tension system so that the temperature of the steam generated is also not uniform; the deformation of the strip and its rapid deterioration, which thus requires considerable maintenance.
Purpose of the present invention is to obtain a method for treating textile material that is quick and economical, and a corresponding treatment apparatus, to attach the dyes or bleaches on every type of textile material under conditions of homogeneous and adjustable pressure higher than atmospheric pressure, which is safe for users.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.